luwra/lib/luwra/stack.hpp

/* Luwra
 * Minimal-overhead Lua wrapper for C++
 *
 * Copyright (C) 2015, Ole Krüger <ole@vprsm.de>
 */

#ifndef LUWRA_STACK_H_
#define LUWRA_STACK_H_

#include "common.hpp"
#include "types.hpp"
#include "internal.hpp"

#include <cassert>
#include <utility>
#include <functional>
#include <string>

LUWRA_NS_BEGIN

namespace internal {
	template <typename T>
	struct Layout {
		static_assert(
			sizeof(T) == -1,
			"Parameter to Layout is not a valid signature"
		);
	};

	template <typename R>
	struct Layout<R()> {
		using ReturnType = R;

		template <typename F, typename... A> static inline
		R direct(State*, int, F&& hook, A&&... args) {
			return hook(
				std::forward<A>(args)...
			);
		}
	};

	template <typename R, typename T>
	struct Layout<R(T)> {
		using ReturnType = R;

		template <typename F, typename... A> static inline
		R direct(State* state, int n, F&& hook, A&&... args) {
			return hook(
				std::forward<A>(args)...,
				Value<T>::read(state, n)
			);
		}
	};

	template <typename R, typename T1, typename... TR>
	struct Layout<R(T1, TR...)> {
		using ReturnType = R;

		template <typename F, typename... A> static inline
		R direct(State* state, int n, F&& hook, A&&... args) {
			return Layout<R(TR...)>::direct(
				state,
				n + 1,
				std::forward<F>(hook),
				std::forward<A>(args)...,
				Value<T1>::read(state, n)
			);
		}
	};
}

/**
 * Retrieve values from the stack and invoke a `Callable` with them.
 *
 * \tparam S Signature in the form of `R(A...)` where `A` is a sequence of types, which shall be
 *           retrieved from the stack, and `R` the return type of `hook`
 * \tparam F An instance of `Callable` which accepts parameters `X..., A...` and returns `R`
 *           (this parameter should be inferable and can be omitted)
 * \tparam X Extra argument types
 *
 * \param state Lua state instance
 * \param pos   Index of the first value
 * \param hook  Callable value
 * \param args  Extra arguments which shall be be passed to `hook` before the stack values
 *
 * \returns Result of calling `hook`
 */
template <typename S, typename F, typename... X> static inline
typename internal::Layout<S>::ReturnType direct(State* state, int pos, F&& hook, X&&... args) {
	return internal::Layout<S>::direct(
		state,
		pos,
		std::forward<F>(hook),
		std::forward<X>(args)...
	);
}

/**
 * Same as `direct(state, 1, hook)`.
 */
template <typename S, typename F, typename... A> static inline
typename internal::Layout<S>::ReturnType direct(State* state, F&& hook, A&&... args) {
	return internal::Layout<S>::direct(
		state,
		1,
		std::forward<F>(hook),
		std::forward<A>(args)...
	);
}

/**
 * A version of [direct](@ref direct) which tries to infer the stack layout from the given
 * `Callable`. It allows you to omit the template parameters since the compiler is able to infer the
 * parameter and return types.
 */
template <typename T> static inline
typename internal::CallableInfo<T>::ReturnType apply(State* state, int pos, T&& obj) {
	return internal::CallableInfo<T>::template RelaySignature<internal::Layout>::direct(
		state,
		pos,
		std::forward<T>(obj)
	);
}

/**
 * Same as `apply(state, 1, obj)`.
 */
template <typename T> static inline
typename internal::CallableInfo<T>::ReturnType apply(State* state, T&& obj) {
	return apply(state, 1, std::forward<T>(obj));
}

namespace internal {
	template <typename T>
	struct LayoutMapper {
		static_assert(
			sizeof(T) == -1,
			"Parameter to LayoutMapper is not a valid signature"
		);
	};

	template <typename... A>
	struct LayoutMapper<void(A...)> {
		template <typename F, typename... X> static inline
		size_t map(State* state, int n, F&& hook, X&&... args) {
			direct<void(A...)>(
				state,
				n,
				std::forward<F>(hook),
				std::forward<X>(args)...
			);
			return 0;
		}
	};

	template <typename R, typename... A>
	struct LayoutMapper<R(A...)> {
		template <typename F, typename... X> static inline
		size_t map(State* state, int n, F&& hook, X&&... args) {
			return push(
				state,
				direct<R(A...)>(
					state,
					n,
					std::forward<F>(hook),
					std::forward<X>(args)...
				)
			);
		}
	};
}

/**
 * Similiar to [direct](@ref direct) but pushes the result of the given `Callable` onto the stack.
 * \returns Number of values pushed
 */
template <typename S, typename F, typename... A> static inline
size_t map(State* state, int pos, F&& hook, A&&... args) {
	return internal::LayoutMapper<S>::map(
		state,
		pos,
		std::forward<F>(hook),
		std::forward<A>(args)...
	);
}

/**
 * Same as `map(state, 1, hook)`.
 */
template <typename S, typename F, typename... A> static inline
size_t map(State* state, F&& hook, A&&... args) {
	return internal::LayoutMapper<S>::map(
		state,
		1,
		std::forward<F>(hook),
		std::forward<A>(args)...
	);
}

LUWRA_NS_END

#endif